Several nose-only systems for the above-defined purpose are known. They are, among others, of the type known as "standard chamber" wherein aerosol flows through a common zone having holes through which the aerosol reaches an animal. Exhaled air and unused aerosol are returned to the same chamber and flow down the chamber to reach the next animal (see e.g. Cannon et al., Am. Ind. Hyg. Assoc. J. 44(12): 923-928 (1883) or U.S. Pat. No. 4,520,808)).
Another system, affording better uniformity of the flow of the substance administered to several animals at once is of a so-called flow-past design. Generally described in the above paper, this system is modified in several patents. For example, U.S. Pat. No. 5,297,502 describes an apparatus for exposing laboratory animals to a gas or vaporous substance directly to the nose of the animals and hence their respiratory system. The apparatus includes concentric inner and outer manifolds. The inner manifold is provided with a plurality of distribution tubes extending radially outward from the manifold, each tube having a horn shaped end. The outer manifold is provided with a plurality of apertured connectors through which the distribution tubes extend. The apertured connectors partially support animal holders such that the nose of an animal within each animal holder is positioned proximate to the horn end of one distribution tube. A gaseous substance is introduced from the lower end of the inner manifold, travels upwardly to the distribution tubes, through the tubes to the animal's noses, then passes through the apertured connectors where it enters the outer manifold. The vaporous substance is drawn upwardly out of the outer manifold.
The known flow-past nose-only units have one inlet pointed directly to the animal's nostrils to favour directional delivery of the substance tested to the respiratory system of the animal.
Other nose-only systems are described in, e.g., U.S. Pat. No. 1,703,087 and U.S. Pat. No. 5,280,784.
It is known that a laboratory animal may sometimes tend to avoid inhalation of the testing substance by trying to curl up (huddle) and withdraw its nose from the point of the delivery of the substance. It is desirable to prevent or minimize such an avoidance response for the sake of uniformity of the experiments.
It is an object of the present invention to optimize the nose-only delivery of the test substance to research animals, and in particular, to provide a system which would mimic a normal, or natural, exposure of the animal to the test substance.
It is another object of the invention to provide an apparatus enabling the exposure of laboratory animals to complex substances, e.g. binary substances, also those with a short lifetime.
It is further an object of the invention to provide a system with a relatively small dead space (space occupied by the unused substance) to enable relatively high concentrations of test substance with the use of relatively small amounts thereof.
It is another object of the invention to provide a nose-only inhalation system wherein the quantity and quality of the substance delivered to an animal under study can be individually controlled.